SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1200 AM CST Sun Nov 29 2020

Valid 291200Z - 301200Z


Isolated strong to severe thunderstorms remain possible today and
tonight across southern portions of the Gulf Coast states into the
eastern Carolinas.  A couple of tornadoes, and a few locally
damaging wind gusts, are the main threats.

An upper low initially over Oklahoma is forecast to move eastward to
the mid/lower Mississippi Valley through the first half of the
period, but will gradually become absorbed by a northern-stream
trough digging east-southeastward out of the northern Plains/upper
Mississippi Valley into the Midwest/middle Mississippi Valley

At the surface, a weak low is forecast to move across the northern
Gulf of Mexico near the Louisiana coast toward Mobile Bay during the
day, along a pre-existing baroclinic zone.  Thereafter, the low is
progged to turn northeastward and move quickly northward along the
Appalachians, deepening rapidly as it reaches the West Virginia
vicinity by the end of the period/Monday morning. 

...Central and eastern Gulf Coast/southeastern Atlantic coast...
Widespread precipitation is forecast to be ongoing at the start of
the period ahead of the advancing upper low, from southern and
eastern Texas across Arkansas and Louisiana into southern
Mississippi and vicinity.  The substantial precipitation and cloud
cover -- that should persist through the day -- over the central
Gulf Coast states/mid South should maintain a stable boundary layer.
 Any potential for surface-based convection appears likely to remain
confined to southeast Louisiana, southeast Mississippi, and into
southern Alabama and the Florida Panhandle through the daylight
hours.  A separate area of storms may evolve during the afternoon
across eastern South Carolina and into the southern Atlantic, near a
developing warm front.  

During the evening and overnight, as the surface low deepens/shifts
rapidly north-northeastward, surface-based convection will spread
eastward across southeastern Alabama and roughly the southern half
of Georgia, and northern portions of the Florida Peninsula ahead of
the strengthening cold front.  Meanwhile, surface-based convection
will shift northward across the eastern Carolinas and eventually
into southeastern Virginia, east of the surface low as the warm
front shifts northward.

Instability is forecast to remain quite limited inland, with
generally less than 300 to 500 J/kg mixed-layer CAPE expected. 
However, increasingly strong and veering flow with height will
evolve with time, in tandem with surface cyclogenesis, yielding
shear profiles sufficient for supercells.  While modest CAPE should
remain a limiting factor, a couple of tornadoes will be possible,
within a broad SLGT risk area from southern Mississippi east to
northern Florida, and north across the eastern Carolinas to
southeast Virginia.  A few stronger storms may also produce
gusty/locally damaging winds, particularly if small bowing segments
can evolve locally.  Risk will taper off from west to east along the
Gulf Coast through the evening, but may linger through the end of
the period across portions of Florida, and particularly along the
Atlantic Coastal portion of the outlook.

..Goss/Moore.. 11/29/2020

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